During the starting process of the synchronous motor, the electromagnet of the stator produces an alternating magnetic field and drags the permanent magnet rotor to oscillate. If the rotor obtains enough kinetic energy, the oscillation amplitude of the rotor will constantly increase, which finally accelerates the rotation of the rotor rapidly to be synchronous with the alternating magnetic field of the stator. For guaranteeing the starting of the traditional synchronous motor, the starting point of the motor is usually set to be lower, which results in that the motor cannot run on a relatively high operating point, and therefore efficiency is lower. In another aspect, the rotor cannot be ensured to rotate in a same direction in every starting since a stop position of the permanent magnetic rotor is unfixed due to characteristics of alternating magnetic field. Accordingly, in applications of fans, water pumps, etc., the impeller driven by the rotor adopts straight type radial blade usually, which results in the lower operational efficiency of the fans, water pumps, etc.